1. Field of the Invention
The present invention relates generally to an apparatus and method for implementing plasma processing on a work piece substrate such as a semiconductor wafer or the like.
2. Description of Related Art
In the field of manufacturing semiconductor devices, a semiconductor treatment apparatus is known for generating magnetron plasma in a vacuum chamber (viz., process chamber). The plasma thus generated is allowed to act on a work piece such as a semiconductor wafer positioned within the vacuum chamber whereby a desired treatment process such as etching and film forming, etc. is performed.
In order to attain satisfactory results, it is necessary to maintain the plasma in a state optimized for a particular process. For this purpose, the magnetron plasma processing apparatus is provided with a magnetic field generator which controls or confines plasma in a desired state.
In order to effectively control or confine plasma, it is known in the art to utilize a multi-pole type magnetic field generator which, by way of example, is disclosed in Japanese Patent Publication No. 2000-306845. In such a type of generator, a plurality of magnets is circularly arranged outside a work piece substrate (e.g. a semiconductor wafer) in a manner that their north and south poles alternate with each other. The wafer is positioned horizontally within the vacuum chamber with the main surface facing upward. With this arrangement, a multi-pole magnetic field is generated at the periphery of a semiconductor wafer placed in the chamber, while no magnetic field is generated above the semiconductor wafer. The number of magnetic poles is equal to four or more than that, and usually selected from a range between eight and forty depending on the required field strength at the periphery of the wafer.
As mentioned above, it is known in the art to utilize a plasma treatment apparatus wherein etching proceeds on a semiconductor wafer using multi-pole magnetic field generated at the periphery of the wafer and maintaining the state of the plasma by appropriately controlling the strength of the multi-pole magnetic field. However, according to the research of the inventors of the instant application it was discovered that there are two contradictory instances in terms of etch rate uniformity across the wafer's surface. In one instance the etch rate uniformity is increased in the presence of multi-pole magnetic field, while in the other instance the etch rate uniformity is increased in the absence of multi-pole magnetic field.
When etching is performed on a silicon dioxide film, the etch rate uniformity is more improved in the presence of a multi-pole magnetic field. In this case, the absence of multi-pole magnetic field causes the etch rate to go high at the wafer's center area and low at the wafer's peripheral area.
On the contrary, when etching is performed on an organic low-dielectric (low-K) film and the like, the etch rate uniformity on the wafer's surface was more improved in the absence of multi-pole magnetic field. In such an instance, the presence of a multi-pole magnetic field causes the etch rate to go low at the wafer's center area and high at the wafer's peripheral region.
If electromagnets are used to generate a multi-pole magnetic field, the start/stop control of the magnetic field generation can be carried out with ease. However, the use of electromagnets is disadvantageous due to their high power consumption and bulkiness. For these reasons, the current practice is to employ permanent magnets. However, A large loading machine is required to mount and dismount permanent magnets on and from the processing apparatus to perform the start/stop control, and accordingly, this involves a long time to operate the machine, resulting in a lowering of the overall working efficiency of semiconductor processing.